Induction heater



' April 8, 1941. E. G. LOFGREN INDUCTION HEATER 2 Sheets-Sheet 1 Filed Aug. 3, 1940 April 1941. E. s. LOFGREN 2,237,569

INDUCTION HEATER Filed Aug. 5. 1940 2 Sheets-Sheet 2 1510672 for 1 11/2621" 6. Lo/fgren By 1223 Aii'orneya Fatented Apr. 8, 1941 UNITED STATES PATENT OFFICE Claims.

This invention relates to electrically actuated heaters and, because of the peculiar structure and operation thereof, is designated as an induction heater. In this heater the major heating action is produced by induction but there is an important minor heating action also produced by radiation and conduction.

Generally stated, the invention consists of the novel devices, combinations of devices, and arrangement of parts hereinafter described and defined in the claims; and it also includes an improved method or process of producing the apparatus or major elements of the heater.

In carrying out the invention, I preferably employ cast iron or similar spool-like core having outstanding flanges to and between which ra-' diating fins are applied. The current conducting element of the heater is a coil wound on the spool. The wire of this coil is of such size that the resistance to the flow of the current will be low so that the said coil will not be brought to a high temperature and only a minor portion of the heating action will be directly radiated therefrom. The current supplied will be an altemating current and the major pontionof the heating action will be produced by alternation or reversal of the magnetic flux that will be produced, not only in the core and its flanges, but in the radlating fins. I

With the above general statements made they will describe a commercial embodiment of the invention illustrated in the accompanying drawings wherein like characters indicate like parts throughout the several views.

Referring to the drawings:

Fig. 1 is a front elevation of the apparatus, some parts being broken away and some parts being sectioned;

Fig. 2 is a front to rear vertical section taken on the line 2-2 of Fig. 1;

Fig. 3 is a horizontal section taken on the line 3-4 of Fig. 2 andv Fig, 4 is a diagrammatic view showing the wiring of the heating system including a thermostat or automatic temperature control.

The heat producing elements of the device are shown as located within sheet metal housing or casing l0 provided with upper and lower louvers l. and I2 and mounted on a base 13. The above referred to coil I4 is wound upon the core l5, preferably of cast iron provided at its ends with flanges l8 that are preferably circular and are set into and rigidly secured in substantially square or rectangular supplemental flanges ll.

These flanges 11 extend both above and below and on both sides of the core and support upper and lower parallel sets of radiating fins or plates I8. The fins or plates l8 are shown as set into grooves in the supplemental flanges I! and, in this preferred arrangement, are vertically disposed below the upper louvers II and above the lower louvers H.

The core and its immediately co-operating elements are supported in the positions stated, by spacing sleeves l9 and co-operatlng screws l9 passed through said sleeves and the walls of the casing and screwed into the supplemental flanges l1.

To produce a forced upward circulation of air around the core and through the spaces between the fins or radiating plates I8, a fan 20, driven by an electric motor 2 I, is located on the base 13.

In the arrangement illustrated, an insulating sleeve 22 is placed around the coil l4 and an additional sleeve or covering 23 is placed around the sleeve 22. These insulating elements, while minor features, are desirable. The sleeve 22 advisably would be a material such as asbestos or glass paper and the element 23 of hard fibre glass or the like.

In the diagram view, Fig, 4, the dotted line 24 indicates a space or enclosure in which the heater is located; 25 indicates a two-wire supply line or circuit, and the numeral 26 indicates a thermostat of the mercury bulb type, the construction and operation of which is Well known. In this arrangement the supply line 25 is crossconnected by a branch circuit 27 and which, by leads 28, 29 and 30, is connected, respectively, to the coil M, the fan motor 2|, and the thermostat 25. A cut-in-and-out switch 3| is located in one side of the main branch circuit 21,

In the arrangement diagrammatically illustrated in Fig. 4, the heater will be rendered operative when switch 3| is closed, but will be rendered active only when the thermostat bulb 26 is tilted, asshown in Fig. 4, thereby simultaneously closing the circuits through said bulb, the fan motor 2|, and the coil M. It is highly important that the fan should be operated simultaneously with closing the circuit through coil l4 and should be cut out of action simultaneously with opening the circuit through said coil. With this arrangement the fan will operate and the air will be forced over the heating elements only when the said heating elements are rendered active.

The heating action produced by this heater has been above indicated in a general way, but a more detailed action is as follows: When the alternating current is closed through the coil I -43, the magnetic flux will be produced not only in the core and its flanges but in the fins or radiating plates it and this rapid alternation of the polarities of the said elements will, as is obvious, induce heat in all of the magnetized elements. Probably the greatest heating action is produced in the spool-like core; and the maximum heat producing action is produced by the rapid alternationsof the polarities of the core, flanges and plates.

In addition to this action induced in the fins or plates, eddy currents will be set up in the core and its flanges and there will be the additional heating action produced .by radiation and conduction of heat from the core to the fins or radieting plates. The above noted features combine to produce a highly emcient heater, the salient novel feature of'which is the arrangement whereby the magnetic flux is conducted to and produced in the flns or radiating plates spaced and located adjacent to but somewhat remotely from the core and main coil.

The improved method of assembling and producing the heater made up of the core, its flanges, its radiating fins or plates, and coil on the spool, is substantially asfollows: First, the spool-like core is casfpreferably from grey iron; next, the coil is wound on the core. Thereafter, the flns or radiating plates and the spool with the coil wound thereon are, by the use of molding cores, brought into the relative positions shown in Fig. 2 and placed in a molder's flask and the extended supplemental flanges H are then cast directly on the flanges of the core and on the ends of the fins or radiating plates. Bythis casting operation the core with its coil, and the radiating 3. The structure defined in claim 1 in further combination with a motor-propelled fan for circulating air around said core and between said radiating plates.

4. The structure defined inclaim 1 in which the radiating plates are arranged in two parallel groups, one on each side of said core, and in further combination with a motor-propelled fan 4 which there is an insulating sleeve applied around said core and coil and anchored to the flanges of said core.

flns and the extended supplemental core flanges will all be very rigidly united. I

When the additional elements indicated at 22 and 23 are employed, they should be assembled aroundthe coil before the casting operation is produced so that the edges of the outer element nected to and supported by said extended flanges I whereby under alternating current applied to said coll, said radiating plates will be subjected to the produced magnetic flux.

'6. The structure defined in claim 1 in which the flanges of said core are provided with independently formed, rigidly anchored extension flanges in which the ends of said radiating plates are anchored.

7. The structure defined in claim 1 in which the radiating plates are arranged in two parallel groups, one on each side of said core, and in which said core is provided with substantially rectangular extension flanges in which the ends of said radiating plates are anchored, one group on diametrically opposite sides of said core.

8. The method of producing a heater assembly of the kind described which consists in applying a coil around a metallic core, assembling in spaced relation a group of heatradiating plates adjacent to said core, and in casting metallic extension flanges on the ends of said core and against the ends of said plates.

9. The method of producing a heater assembly of the kind described which consists in applying a coil around the body of a spool-like metallic core, in assembling a group of spaced heat radlating plates adjacent and parallel to said core, and thereafter casting metallic supplemental flanges on the end flanges of said spool-like'core and against the ends of said plates.

10. The method of producing a heater assembly of the kind described which consists in applyinga coil around the body of said spool-like core, in assembling two groups of spaced heat radiating plates in parallel relation to but on diametrically opposite sides of said core, and in thereafter casting supplemental flanges on the end flanges of said core and against the ends of 2. The structure defined in claim 1 in which the radiating plates are arranged in two parallel I groups, one on each side of said core.

said radiating plates.

EINAR G. LOFGREN. 

